1. Field of the Invention
The present invention relates to a force multiplier for multiplying the force applied onto a driving lever and for transmitting the force multiplied to a driven lever to generate a high press force on a follower of the driven lever.
2. Description of the Prior Art
Conventionally, there has been widely used a crank-pin mechanism as shown schematically in FIG. 20 or a toggle-joint mechanism as shown schematically in FIG. 21 for a driving mechanism of an auto-drive press machine which acts as a force multiplier.
As is well known to those skilled in the art, the output press force P of a slider 1 or 2 for pressing a workpiece (not shown) is inversely proportional to the velocity V thereof: P.multidot.V=K (wherein K is a constant proportional to an energy applied exteriorly). In this context, it is desirable to decrease the velocity of the slider upon pressing the work as low as possible in order to obtain a larger press force.
However, the velocity of the slider 1 of the press with a crank-pin mechanism, when the crank-pin is driven at a constant velocity, is varied so as to depict a sine curve as shown by a velocity distribution V'.sub.1 in FIG. 20 and, therefore, the velocity remains relatively high even during the press stroke of the slider. For this reason, the magnification of force obtained in the press mentioned above is relatively small. In other words, it is impossible to obtain a high press force without increasing the energy to be applied exteriorly and/or without enlarging the size of the press. Moreover, large noises and strong oscillations are generated upon pressing the work since the press tool cooperating with the slider strikes the work at a relatively high velocity. These lower the working accuracy to the work and shorten the life of the tool.
In the press with the toggle-joint mechanism, as shown in FIG. 21, the velocity distribution V'.sub.2 of the slider 2 is so improved as to give a velocity relatively lower than that of the velocity distribution V'.sub.1 during the press stroke. But the ratio of reduction in the velocity remains several tens % at most.
The inventor of the present invention has proposed one new mechanism for the force multiplier in the Japanese Patent Application No. 226200/1983 which corresponds to the Japanese Patent Laid Open Publication No. 121356/1985.
FIG. 22 shows an example according to said new mechanism proposed.
As shown in FIG. 22, the mechanism is comprised of a circular disk 3 being supported in a hole 4 of a supporting frame 5 rotatably about the center thereof, a driving lever 6 being formed extended from the peripheral portion of said circular disk in the radial direction thereof, and a driven lever 7 having a pin 8 as a follower at one end portion thereof which is supported pivotably by an axis 9 on the supporting frame at the other end thereof, said pin 8 being fitted into a groove 10 as a guide means which is formed on the circular disk in the radial direction thereof. As is shown in FIG. 22, the distance defined between the center 02 of the pin 8 is so determined as to be longer by a predetermined small distance e than the distance r defined between the center 01 of the axis 9 and the center 0 of the circular disk 3.
According to this mechanism, when the driving lever 6 is operated to pivot from the initial position indicated by an arrow (A) toward the final position indicated by an arrow (B), the pin 8 as a follower is moved sliding in the groove 10 from the radially outer position toward the center 0 of the circular disk 3 and, therefore, the driven lever 7 is driven to pivot from the initial position (A') toward the final position (B'). The velocity of the pin 8 is decelerated rapidly as it approaches to the center 0 of the circular disk 3. In FIG. 23, the velocity distribution V' of the pin is shown. As is apparent from the velocity distribution V', the velocity of the pin becomes very slow in the press stroke of the slider being coupled to the pin as a follower. Accordingly, an amazingly high magnification of the force can be obtained according to the proposed mechanism and impact force upon pressing can be reduced considerably.
Although this mechanism has supreme advantages when compared with the conventional mechanism as mentioned above, it has still some structural problems to be improved. One of them is that the follower is guided to slide in the groove of the circular disk. Especially, the direction of the force P applied to the follower in the groove becomes substantially perpendicular to the direction of slide of the follower when it approaches to the center of the circular disk. In other words, the friction force against the follower becomes very large to cause a rapid wear of the follower.